Multi-dimensional optical spectroscopy has developed as a method for characterizing materials in a variety of applications from biomedical applications to the semiconductor industry. To this point, though making a substantial mark with contributions to molecular and reaction dynamics, optical techniques have been limited due to the degree of complexity and expertise required for construction and use of the optical and infrared 2D FT spectrometers.
Typical 2D spectrometers require the use of four variably delayed pulses in which three beams are aligned in a “boxcar” geometry to achieve background-free phase matching of the 2D signal as shown in FIG. 1. The fourth is used for external heterodyne detection of the signal field for acquiring phase and amplitude information. Commonly, a fifth beam is introduced and aligned in the forth corner of the “boxcar” to help with alignment of the signal field and for acquisition of the pump-probe measurements that can be used for properly processing 2D data. The final 2D spectrum contains two frequency axes in which the excitation of a molecular transition along one axis, ω12t, can be correlated with an emission along the other dimension, ω34. Therefore, well defined phase relationships between the first two interactions and between the third and fourth interaction are required to properly retrieve molecular information. Acquisition of spectra by this method requires a large degree of post processing or “phasing” after collection.
There is a continuing need, however, for improvements in the measurement of two dimensional spectra.